Minerals
and their usage
Internet
exercise
To define minerals we use their Physical Properties in the
field or the lab. The following list shows the known and used properties.
Color
Streak
Luster
Hardness
Cleavage or Fracture
Crystalline Structure
Magnetism
Reaction with hydrochloric acid
1.
Color
Minerals usually
have a distinctive color that can be used for identification.
Translucent to transparent minerals however have a
varied degree of color due to the presence of trace minerals (Exotic
coloration). Therefore, color alone is not reliable as a single identifying
characteristic.
In opaque minerals, the color tends to be more
consistent, so learning the colors associated with these minerals can be very
helpful in identification.
Use your
favorite search engine to learn about the exotic coloration of minerals, collect
thumbnail pictures and names of examples of the same mineral with different
color. And tell me what trace element causes the color?
Find at least
three minerals with varying coloration, and at least three colors for each and
their names also figure out the cause of the color?
2.
Streak
Streak is the color of the mineral in powdered
form. Streak shows the true color of the mineral. In large solid form, trace
minerals can change the color appearance of a mineral by reflecting the light in
a certain way. Trace minerals have little influence on the reflection of the
small powdery particles of the streak. The streak of metallic minerals tends to
appear dark because the small particles of the streak absorb the light hitting
them. Non-metallic particles tend to reflect most of the light so they appear
lighter in color or almost white.
Because streak is a more accurate illustration of
the mineral’s color, streak is a more reliable property of minerals than color
for identification.
What tool do we use to define the streak of the
mineral?
Please use your search engine to find 5 different
minerals with characteristic streak color. Collect a thumbnail picture for each!
3.
Luster
Luster is the property
of minerals that indicates how much the surface of a mineral reflects light. The
luster of a mineral is affected by the brilliance of the light used to observe
the mineral surface. Luster of a mineral is described in the following terms:
Metallic The mineral is opaque and
reflects light as a metal would.
Submettalic The mineral is opaque and dull. The mineral is dark colored.
Nonmettalic: The mineral does not
reflect light like a metal. Nonmetallic minerals are described using modifiers
that refer to commonly known qualities. Here is a list you can use:
adamantine: brilliant, e.g. diamond
vitreous: glassy
resinous: appearance similar to resins or saps of certain trees or shrubs
greasy: like oil on glass
pearly: pearl
silky: like silk, usually fibrous textures
earthy: like dirt
Please collect
thumbnail pictures for each type of luster with name.
4.
Hardness
Hardness is one of the
better properties of minerals to use for identifying a mineral. Hardness is a
measure of the mineral’s resistance to scratching. The Mohs scale is a set of 10
minerals whose hardness is known. The softest mineral, talc, has a Mohs scale
rating of one. Diamond is the hardest mineral and has a rating of ten. Softer
minerals can be scratched by harder minerals because the forces that hold the
crystals together are weaker and can be broken by the harder mineral.
The following is a
listing of the minerals of the Mohs scale and their rating:
Use your
favorite search engine what kind of easy tools can we use to identify the
hardness of the different minerals?
Find the
hardness of the following minerals:
k-feldspar:
garnet:
muscovite:
graphite
ruby
topaz
aquamarine
5.
Cleavage/fracture
Minerals tend to break
along lines or smooth surfaces when hit sharply. Different minerals break in
different ways showing different types of cleavage.
Cleavage is defined
using two sets of criteria. The first set of criteria describes how easily the
cleavage is obtained. Cleavage is considered perfect if it is easily obtained
and the cleavage planes are easily distinguished. It is considered good if the
cleavage is produced with some difficulty but has obvious cleavage planes.
Finally it is considered imperfect if cleavage is obtained with difficulty and
some of the planes are difficult to distinguish.
The second set of
criteria is the direction of the cleavage surfaces. The names correspond to the
shape formed by the cleavage surfaces and are defined specifically by the angles
of the cleavage lines as indicated in the chart below:
Please collect thumbnail pictures and names of
minerals with the given type of cleavages
Cubic Cleavage:
Rhombohedral cleavage:
Octahedral Cleavage:
Basal Cleavage:
Prismatic cleavage:
Fracture describes the
quality of the mineral’s broken surface. Most minerals display either uneven or
grainy fracture, conchoidal (curved, shell-like lines) fracture, or hackly
(rough, jagged) fracture.
Please collect a thumbnail picture and the name of
the mineral with each type of fracture.
6.
Crystalline Structure
Minerals occur in various shapes and sizes. The
particular shape is determined by the arrangement of the atoms, molecules or
ions that make up the crystal and how they are joined. This is called the
crystal lattice. If there is no crystalline structure, it is called amorphous.
However, there are very few amorphous crystals and these are only observed under
extremely high magnification.
We classify crystals into six different systems based on symmetry. To do this
without the aid of an optical microscope or x-rays, the mineral must have grown
with crystal faces present. The planar surfaces resulting from crystal growth
may be distinguished with care from cleavage surfaces by the presence of
impurities, growth striations, or tarnish (lack of fresh look) upon the growth
surface. Since crystal faces are a reflection of an orderly internal atomic
arrangement, there is a possibility that the planes they represent are also
planes of weakness and cleavage.
Please collect thumbnail pictures of at
least 5 different minerals typical crystal forms.
7.
Magnetism
Magnetic susceptibility
Diamagnetic minerals-
minerals not attracted by a magnet.
Paramagnetic minerals -
minerals attracted by a magnet.
Please find thumbnail picture and name for minerals
which are paramagnetic. Why would a mineral be paramagnetic?
8.
Reaction with hydro-chloric acid
Certain minerals will
effervesce (bubble) when dilute hydrochloric acid is applied to the surface.
This is characteristic of those minerals containing the carbonate anion
CaCO3 + 2HCl
= CaCl2 + H2O + CO2 (gas).
The amount of
effervescence depends upon how soluble the mineral is (calcite vs. dolomite)
Please figure out which mineral will effervesce the
most and least?
Minerals and how do we use them
Use the following
internet site:
http://geology.com/minerals/ and collect thumbnail pictures and information
(color, hardness, cleavage, luster, streak) about the following minerals (Best
is if you make up a table by hand) :
1.
Quartz
2.
Chert
3.
K-feldspar
4.
Ca-Plagioclas
5.
Na-Plagioclase
6.
Olivine
7.
Pyroxene
8.
Amphibole
9.
Biotite
10.
Muscovite
11.
Kaolinite
12.
13. Garnet
14. Calcite
15. Dolomite
16. Halite
17. Gypsum
18. Magnetite
19. Fluorite
20. Galena
21. Pyrite
22. Hematite
23. Graphite
24. Bauxite